Technical Field
Embodiments of the subject matter disclosed herein generally relate to methods and systems and, more particularly, to mechanisms and techniques for performing a marine seismic survey using autonomous underwater vehicles (AUVs) that carry appropriate seismic sensors and use one or more guiding AUVs for navigation.
Discussion of the Background
Marine seismic data acquisition and processing generate a profile (image) of a geophysical structure under the seafloor. While this profile does not provide an accurate location of oil and gas reservoirs, it suggests, to those trained in the field, the presence or absence of these reservoirs. Thus, providing a high-resolution image of geophysical structures under the seafloor is an ongoing process.
Reflection seismology is a method of geophysical exploration to determine the properties of earth's subsurface, which is especially helpful in determining the above-noted reservoirs. Marine reflection seismology is based on using a controlled source of energy that sends energy into the earth. By measuring the time it takes for the reflections and/or refractions to come back to plural receivers, it is possible to evaluate the depth of features causing such reflections. These features may be associated with subterranean hydrocarbon deposits.
A traditional system for generating seismic waves and recording their reflections off the geological structures present in the subsurface uses at least one large vessel that tows an array of seismic receivers provided on streamers. The vessel also tows a seismic source array configured to generate seismic waves. The seismic waves propagate downward toward the seafloor and penetrate it until a reflecting structure (e.g., reflector) eventually reflects the seismic waves. The reflected seismic waves propagate upward until they are detected by the receiver(s) on the streamer(s). Based on the data collected by the receiver(s), an image of the subsurface is generated.
However, this traditional configuration is expensive because the cost of streamers and the cost of operating this system are high. In addition, this conventional technology acquires the seismic data with considerable noise because of the receivers' closeness to the water surface and due to the noise that propagates through the streamers.
New technologies (see, e.g., patent application Ser. Nos. 14/440,241 and 14/104,376, both belonging to the assignee of this application, the content of which is incorporated by reference into this application) deploy plural AUVs for collecting the seismic data at a greater depth than the streamers. However, maintaining the plural AUVs along desired travel paths have been shown to be challenging.
Accordingly, it would be advantageous to provide a navigation system for the plural AUVs so that each of them follows a desired path.